FIG. 1 schematically illustrates a conventional dual-band antenna. The dual-band antenna is formed on a two-layer printed circuit board (PCB). For example, the dual-band antenna is formed on a top layer of the printed circuit board, and a metal ground surface 130 is formed on a bottom layer of the printed circuit board. Moreover, a radiation element of the dual-band antenna is formed on an antenna clearance region 110.
As shown in FIG. 1, the node A is an antenna feed port of the radiation element. The conducting path P1 extended from the node A is a high-frequency resonant path. The conducting path P2 extended from the node A is a low-frequency resonant path. The two operating frequencies of the radiation element are determined according to the lengths of the two conducting paths P1 and P2.
For example, the wavelength of the higher operating frequency is λ1, and the wavelength of the lower operating frequency is λ2. Consequently, the length of the conducting path P1 is equal to (¼)λ1, and the length of the conducting path P1 is equal to (¼)λ2.
FIG. 2 schematically illustrates a conventional coplanar waveguide dual-band antenna. The coplanar waveguide dual-band antenna, which is also referred as a CPW dual-band antenna, is formed on a single-layer printed circuit board. The radiation element of the dual-band antenna is formed on an antenna clearance region 210. Moreover, two metal ground surfaces 230a and 230b are formed on the printed circuit board. Moreover, the two metal ground surfaces 230a and 230b are located at two sides of the dual-band antenna, respectively.
As shown in FIG. 2, the node B is an antenna feed port of the radiation element. The conducting path P3 extended from the node B is a high-frequency resonant path. The conducting path P4 extended from the node B is a low-frequency resonant path.
For example, the wavelength of the higher operating frequency is λ3, and the wavelength of the lower operating frequency is λ4. Consequently, the length of the conducting path P3 is equal to (¼)λ3, and the length of the conducting path P4 is equal to (¼)λ4.
FIG. 3 schematically illustrates another conventional dual-band antenna. The dual-band antenna is disclosed in U.S. Pat. No. 6,801,168. The dual-band antenna is formed on a two-layer printed circuit board. A first radiation element of the dual-band antenna is formed on a top layer of the printed circuit board. A second radiation element and a metal ground surface 330 are formed on a bottom layer of the printed circuit board. Moreover, the first radiation element is formed on an antenna clearance region of the top layer of the printed circuit board, and the second radiation element is formed on an antenna clearance region of the bottom layer of the printed circuit board.
As shown in FIG. 3, the node C is an antenna feed port of the dual-band antenna. The conducting path P5 extended from the node C is a low-frequency resonant path. The second radiation element is contacted with the metal ground surface 330. The conducting path P6 extended from the metal ground surface 330 is a high-frequency resonant path.
FIG. 4 schematically illustrates another conventional dual-band antenna. The dual-band antenna is disclosed in US Patent Publication No. 20040108957. The dual-band antenna is formed on a two-layer printed circuit board. A first radiation element 412 and a second radiation element 414 of the dual-band antenna are formed on a top surface of the printed circuit board. Especially, the first radiation element 412 and the second radiation element 414 of the dual-band antenna are formed on an antenna clearance region of the top surface of the printed circuit board.
As shown in FIG. 4, the node D is an antenna feed port of the dual-band antenna. The conducting path P7 extended from the node D is a high-frequency resonant path. The conducting path P8 of the second radiation element 414 is a low-frequency resonant path.